Ultra-wideband (UWB) includes technology having a bandwidth larger than 500 MHz or 25 percent of a center frequency. Contemporary interest exists in development of wireless versions of serial technologies, such as universal serial bus (USB), capable of UWB transmission rates due to the proliferation of USB-adapted devices in various computational and media systems.
In digital communications, binary data is transmitted by designing a set of unique signals corresponding to individual messages. The ultimate limit of communications performance over a wireless channel is known as the channel capacity. For a given signal-to-noise ratio (SNR), channel capacity provides the highest data rate that can reliably be achieved. Conversely, for a given data rate, it provides the minimum SNR for reliable communication.
Error-correcting codes, used in conjunction with digital modulation, are widely used to provide robust communication over wireless channels. The transmitter in these wireless systems adds redundancy to the data prior to transmission. An analog carrier is then modulated with the coded signal and transmitted over the channel. The receiver demodulates the data and uses the redundancy in the data stream to decode the data in the presence of channel impairments.
Signal shaping is the process of changing the probability distribution of the transmitted signal to one that is closer to the ideal for the channel at hand. Most communication systems are typically impaired by Gaussian noise. For this type of impairment, the distribution of the transmitted signal should ideally be Gaussian.
A communication system can only achieve the capacity of the channel through a combination of error-correction coding and signal shaping. Even an optimal error-correcting code, which does not exist in practice, can get no closer than 1.53 dB from capacity, without signal shaping. Practical coding techniques, including bit-interleaved coded modulation, trellis-coded modulation, multi-level codes, Low Density Parity check (LDPC) codes, and turbo codes are bounded even further away from capacity.